The aim of this work is to find the mechanism(s) by which adrenal catecholamine secretion is stopped. Calcium is known to initiate the response, but the disposition of this "activator" calcium is still not clear. Experiments will be done to determine what happens to the calcium after it initiates secretion. Also attempts will be made to modify adrenal catecholamine secretion using drugs or metallic cations and then to determine how these changes modify calcium metabolism of adrenal cells.